Hydrostatic Flapper Stimulation Valve and Method

ABSTRACT

A downhole tool including a tubular housing, a sleeve, a flapper valve, and a pressurized chamber. The tubular housing has an inner bore. The sleeve is disposed in the inner bore and configured to slide between a first position and a second position. The flapper valve is pivotally coupled to the tubular housing, maintained in an inoperative position when the sleeve is in the first position, and pivotable between an open position and a closed position when the sleeve is in the second position. The pressurized chamber is in fluid communication with the sleeve, wherein, upon activation of the downhole tool, a hydrostatic pressure is applied on the sleeve via the pressurized chamber, such that the sleeve slides from the first position to the second position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Applicationhaving Ser. No. 61/291,216, filed on Dec. 30, 2009, which isincorporated by reference herein.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention generally relate to isolationvalves in wellbore completions. More particularly, embodiments of thepresent invention relate to flapper valves for isolating one casingregion from another.

2. Description of the Related Art

Fracturing techniques in wellbores have been used to extract fluids,such as hydrocarbons like natural gas, from wellbores that wouldotherwise be unproductive. In situations where multiplehydrocarbon-bearing zones are encountered in vertical wells, horizontalwells, or in deviated wells, the multiple zones can be fractured oneafter another. This can be accomplished by perforating and thenfracturing a distal zone and placing a bridge plug in the casingimmediately above the fractured distal zone. This can isolate thefractured distal zone, allowing an adjacent proximal zone to beperforated and fractured. This process can be repeated until all of thedesired zones have been fractured.

Once all the desired zones have been fractured, the bridge plugs betweenadjacent zones can be destroyed or opened to allow fluids from thefractured zones to flow in a commingled stream up the tube string to thesurface. To accomplish this, the plugs can be broken apart or drilledout to allow the flow of fluid; however, this can leave fouling debrisin the tube string and can present difficulties especially in deviatedwells. Some plugs can instead be dissolved using activating agents, butthis can limit the fluids that can be used with the downhole tool orpresent challenges if other dissolvable elements are used in thewellbore that are not intended to dissolve at the same time as the plug.The plugs can also be check valves, such as flapper valves, but thecheck valves need to be maintained in the open position duringdeployment down the well and thus require manipulation to allow them tooperate at the desired time. This manipulation can require expensiveequipment and can delay the sequential fracturing process. What isneeded is a bridge plug that can effectively isolate the multiple zones,which can be deployed and removed without suffering from the drawbacksdescribed above or others.

SUMMARY

Embodiments of the disclosure can provide an illustrative downhole tool,which can include a tubular housing, a sleeve, a flapper valve, and apressurized chamber. The tubular housing can have an inner bore. Thesleeve can be disposed in the inner bore and can be configured to slidebetween a first position and a second position. The flapper valve can bepivotally coupled to the tubular housing, maintained in an inoperativeposition when the sleeve is, for example, in the first position, andpivotable between an open position and a closed position when the sleeveis, for example, in the second position. The pressurized chamber can bein fluid communication with the sleeve, wherein, upon activation of thedownhole tool, a hydrostatic pressure can be applied on the sleeve viathe pressurized chamber such that the sleeve can slide from the firstposition to the second position.

Embodiments of the disclosure can also provide an illustrative method ofplugging a casing string with a flapper valve assembly. The method caninclude storing a flapper valve in a stowed position with a sleeve, andbiasing the flapper valve toward a valve seat. The method can alsoinclude longitudinally moving the sleeve by applying a hydrostaticpressure differential across the sleeve to release the flapper valvefrom the stowed position, and selectively blocking a flow of fluidthrough the casing string with the flapper valve.

Embodiments of the disclosure can further provide an illustrativeflapper valve assembly, which can include a tubular housing, a sleeve, aflapper valve, and a pressurized chamber. The tubular housing can beconnectable to a wellbore casing string and can have a storage cavitydefined therein. The sleeve can be slidable between a first position anda second position, wherein the sleeve in the first position can coverthe storage cavity and the sleeve in the second position can at leastpartially uncover the storage cavity. The flapper valve can be disposedin the tubular housing and can be pivotally connected thereto. Theflapper valve can be contained in the storage cavity, for example, whenthe sleeve is in the first position, and the flapper valve can bepivotable between an open position and a closed position, for example,when the sleeve is in the second position. The pressurized chamber canbe configured to create a pressure differential across at least aportion of the sleeve such that the sleeve can move longitudinally fromthe first position to the second position.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 depicts a cross-sectional view of an illustrative flapper valveassembly, showing an illustrative flapper valve in a stowed position,according to one or more embodiments described.

FIG. 2 depicts a view similar to FIG. 1, showing the illustrativeflapper valve blocking a downward flow of fluid into a well, accordingto one or more embodiments described.

FIG. 3 depicts a cross-sectional view of another illustrative flappervalve assembly, according to one or more embodiments described.

FIG. 4 depicts a cross-sectional view of yet another illustrativeflapper valve assembly, according to one or more embodiments described.

DETAILED DESCRIPTION

A detailed description will now be provided. Each of the appended claimsdefines a separate invention, which for infringement purposes isrecognized as including equivalents to the various elements orlimitations specified in the claims. Depending on the context, allreferences below to the “invention” may in some cases refer to certainspecific embodiments only. In other cases it will be recognized thatreferences to the “invention” will refer to subject matter recited inone or more, but not necessarily all, of the claims. Each of theinventions will now be described in greater detail below, includingspecific embodiments, versions and examples, but the inventions are notlimited to these embodiments, versions or examples, which are includedto enable a person having ordinary skill in the art to make and use theinventions, when the information in this disclosure is combined withavailable information and technology.

The terms “up” and “down”; “upward” and “downward”; “upper” and “lower”;“upwardly” and “downwardly”; “above” and “below”; and other like termsas used herein refer to relative positions to one another and are notintended to denote a particular spatial orientation since the apparatusand methods of using the same can be equally effective in eitherhorizontal or vertical wellbore uses.

FIGS. 1 and 2 depict an illustrative flapper valve assembly 30 that canconnect to a casing string as part of a wellbore completion (not shown),according to one or more embodiments. The flapper valve assembly 30 canhave a flapper valve 67, a sleeve 70, and a pressurized chamber 71. Thesleeve 70 can be slidable between a first position, shown in FIG. 1, anda second position, shown in FIG. 2. In the first position, the sleeve 70can store the flapper valve 67 in an inoperative state or position,which can also be referred to herein as a stowed position. The flappervalve 67 can be maintained in the inoperative position, for example,during deployment of the casing string to which the flapper valveassembly 30 can be attached. In the second position, the sleeve 30 canrelease the flapper valve 67 into an operative state, allowing theflapper valve 67 to block a flow of fluid in at least one direction. Thepressurized chamber 71 can enable the movement of the sleeve 70 byhydrostatic force, without requiring mechanical manipulation of thesleeve 70.

The flapper valve assembly 30 can also include a tubular housing 68,which can have an inner bore 69 and a lower sub 72. The lower sub 72 canhave a threaded lower end 74 that can match the threads of any pipejoints or collars that can be included in a wellbore completion alongwith the flapper valve assembly 30. The tubular housing 68 can also havea central sub 76 coupled to the lower sub 72 and to an upper sub 80, forexample, using threaded connections. In one or more embodiments, theupper sub 80 can be threaded onto the central sub 76 using a connectingmember 79 and can provide a threaded end 84 that can attach to thecasing string (not shown). The upper sub 80 can also include asmooth-walled portion 86 of the inner bore 69. The sleeve 70 can includea piston 90 connected thereto or integrally-formed therewith. The piston90 can include one or more o-rings and/or other sealing devices tocreate slidable and sealing engagement between the piston 90 and thesmooth-walled portion 86 of the tubular housing 68.

In one or more embodiments, the flapper valve 67 can be pivotallycoupled to the lower sub 72 with a biasing member 109. In one or moreembodiments, the flapper valve 67 can be biased toward the closedposition by the biasing member 109. The biasing member 109 can include apivot pin-and-spring assembly, or in other embodiments, can include anybiasing structure or configuration. The biasing member 109 can bias theflapper valve 67 toward the lower sub 72 (counterclockwise, as shown),specifically, toward a valve seat 120 defined in the lower sub 72. Whilethe sleeve 70 remains in the first position, however, the flapper valve67 can be maintained inoperative in the stowed position.

The sleeve 70 can include a lower section 102 that can have a smallerexternal diameter than the tubular housing 68 and can thereby provide astorage cavity 88 for the flapper valve 67 radially between the sleeve70 and the tubular housing 68. In the first position, a lower end of thesleeve 70 can engage the lower sub 72, as shown in FIG. 1, and canthereby seal against the lower sub 72 so that any materials proceedingthrough the inner bore 69 can be prevented from entering the storagecavity 88 and interfering with operation of the flapper valve 67.

The pressurized chamber 71 can be disposed in the upper sub 80 or, inother embodiments, can be disposed radially outside of the upper sub 80(not shown). The pressurized chamber 71 can contain a gas at a reducedpressure in relation to the pressure in the flapper valve assembly 30below the flapper valve 67. For example, the pressurized chamber 71 caninclude air at or near surface pressure, which can be encased therein.In one or more embodiments, the pressurized chamber 71 can be enclosedor self-contained. In one or more embodiments, the pressurized chamber71 can communicate with the surface (not shown) when deployed down awellbore (not shown) such that the surface can be the source of thereduced pressure gas contained in the pressurized chamber 71. In one ormore embodiments, the pressurized chamber 71 can be located below theflapper valve 67 in the lower sub 72.

The pressurized chamber 71 can be in communication with a piston chamber73 via a line 75, which can be formed in the upper and central subs 80,76, with the line 75 extending past the connecting member 79, forexample. The piston chamber 73 can be defined between the lower sub 72and the piston 90, adjacent a side of the piston 90, as shown. In one ormore embodiments, when the sleeve 70 is in the first position, thepiston 90 can engage the lower sub 72 such that the piston chamber 73can have little or substantially no volume. A second chamber 77 can beformed, for example, above the piston 90 and adjacent an opposite sideof the piston 90, i.e., across the piston 90 from the piston chamber 73.The second chamber 77 can be separated and/or isolated from the innerbore 69 by the sleeve 70 such that, in one or more embodiments, thesecond chamber 77 can be prevented from communicating with the innerbore 69 and the piston chamber 73. In one or more embodiments, thesecond chamber 77 can initially be held at substantially the samepressure as the piston chamber 73 such that there can be substantiallyno pressure differential across the piston 90, for example.

The flapper valve assembly 30 can be activated to block a flow of fluidthrough the inner bore 69. Upon activation, the sleeve 70 can be drawnupward to the second position shown in FIG. 2 from the first positionshown in FIG. 1, for example, thereby releasing the flapper valve 67 tothe operative state. To draw the sleeve 70 upward, a vented section 110of the tubular housing 68 can be created after the flapper valveassembly 30 has been positioned at a desired location, for example. Invarious embodiments, the vented section 110 can be created by anysuitable perforating operation, including but not limited to: mechanicalpuncture, sand jetted puncture, ballistics such as shaped charges, byhydraulically or otherwise applying pressure to a frangible materialsuch that the frangible material breaks apart, and/or by dissolving adissolvable material. In various other embodiments, any other suitablemethod of perforating the tubular housing 68 and/or otherwise creatingthe vented section 110 can be used. Furthermore, the vented section 110can extend partially through the tubular housing 68 to the extentnecessary to put the pressurized chamber 71 in communication with theinner bore 69. Although not shown, in one or more embodiments, thevented section 110 can extend completely through the tubular housing 68.

In one or more embodiments, the flapper valve 67 can be pivotallycoupled to the lower sub 72 with a biasing member 109. In one or moreembodiments, the flapper valve 67 can be biased toward the closedposition by the biasing member 109 such that when the sleeve 70 slidesto the second position, for example, the flapper valve 67 can be urgedtoward the valve seat 120 by the biasing member 109. The biasing member109 can include a pivot pin-and-spring assembly, or in otherembodiments, can include any biasing structure or configuration.

The second chamber 77 can be defined between the piston 90 and the uppersub 80 such that, for example, while the sleeve 70 moves toward thesecond position, the volume of the second chamber 77 can beprogressively reduced. In the second position, the sleeve 70 can releasethe flapper valve 67, allowing the biasing force of the biasing member109 to act thereon and urge the flapper valve 67 toward the valve seat120, for example. Accordingly, in the operative state, the flapper valve67 can move or pivot as shown by arrow 97 between a closed position anda range of open positions. In the closed position, the flapper valve 67can sealingly engage the valve seat 120. Furthermore, the flapper valve67 can be in the closed position when, for example, the force applied onthe flapper valve 67 by the pressure from above plus the biasing forceof the biasing member 109 is greater than the force applied on theflapper valve 67 from below.

In one or more embodiments, the flapper valve 67 can have a concave orsaddle-shaped upper and/or lower face, such that, for example, across-section of the flapper valve 67 can be arcuate. The flapper valve67 in the inoperative state can thus conform to the annularcross-section of the tubular housing 68 and/or the storage cavity 88.This can allow the flapper valve assembly 30 to avoid significantlyobstructing or decreasing a flow path area of the casing string to whichthe flapper valve assembly 30 can be attached. In one or moreembodiments, the sleeve 70 can have an inner diameter that can besubstantially the same as a diameter of the inner bore 69 proximal theupper and/or lower subs 80, 72, as shown. Furthermore, the flapper valve67 being saddle-shaped can aid in resisting the pressure appliedthereon, e.g., from above.

The valve seat 120 can also be concave or inversely saddle-shaped, so asto mate with the flapper valve 67 and create a sealing engagementtherewith. Additionally, the flapper valve 67 can be made of a frangiblematerial and can be movably fixed to the tubular housing 68 in anysuitable manner. In one or more embodiments, the flapper valve 67 can besimilar to or the same as the flapper valve described in U.S. patentapplication Ser. No. 12/130,840, the entirety of which is incorporatedby reference herein to the extent it is not inconsistent with thisdisclosure.

With the sleeve 70 in the second position, the flapper valve 67 can belocated at any of a range of open positions between the valve seat 120and the tubular housing 68 (e.g., pivoted, shown clockwise, from thevalve seat 120 toward the tubular housing 68), and can thereby allow aflow of fluid upward through the flapper valve assembly 30. The flappervalve 67 can be in the open position when the pressure from belowapplies a force on the flapper valve 67 greater than the force appliedby pressure from above plus the biasing force, for example. Further, theflapper valve 67 can move or pivot between a range of open positions, asshown by the arrow 97, depending, for example, on the magnitude of thepressure differential across the flapper valve 67. Thus, a greaterpressure from below can open the flapper valve 67 to a greater extent,for example.

In at least one embodiment, the flapper valve assembly 30 can beactivated to release the flapper valve 67 from the stowed position. Toactivate the flapper valve assembly 30, the tubular housing 68 can beperforated or vented by any means known in the art, as described above,which can thereby expose the pressurized chamber 71 to the inner bore 69via the vented section 110. The pressure in the inner bore 69 can begreater than the pressure previously in the pressurized chamber 71. Thisgreater pressure from the inner bore 69 can then be communicated throughthe vented section 110, through the pressurized chamber 71 and the line75, to the piston chamber 73, and can thereby increase the pressure inthe piston chamber 73. This can create a pressure differential acrossthe piston 90, as the second chamber 77 can remain at the reducedpressure. The pressure differential can draw the piston 90, andtherefore the sleeve 70, upward toward the upper sub 80, for example. Inone or more embodiments, the second chamber 77 can include any vents asnecessary to allow the contents (e.g., air) therein to escape as thepiston 90 moves toward the shoulder 96. In one or more embodiments, thecontents of the second chamber 77 can escape between the piston 90 andthe smooth-walled portion 86. In one or more embodiments, venting thesecond chamber 77 can be unnecessary, as the pressure differentialbetween the second chamber 77 and the piston chamber 73 can besufficiently great to move the piston 90, despite the pressure increasesin the second chamber 77 resulting from the volume of the second chamber77 decreasing.

The drawing of the sleeve 70 upward via a pressure differential acrossthe piston 90 can also be described as releasing the hydrostaticpressure in the inner bore 69. Thus, upon activation, the sleeve 70 canbe moved to the second position by simply perforating the tubularhousing 68, without requiring mechanical manipulation or engagement ofthe sleeve 70. The hydrostatic pressure can thus draw the sleeve 70 fromthe first position (FIG. 1) to the second position (FIG. 2), forexample.

In one or more embodiments, while the sleeve 70 slides from the firstposition to the second position, the flapper valve 67 can beprogressively exposed and can eventually be released into the operativestate. Accordingly, after entering the operative state, the flappervalve 67 can initially pivot to a closed position, blocking a flow offluid in a first direction (e.g., downward, as shown), which can isolateportions of the wellbore completion below the flapper valve assembly 30from portions above it. Furthermore, the flapper valve 67 can pivot tothe open position, allowing an upward flow of fluid. In this manner, forexample, the flapper valve 67 can selectively block fluid flowingtherethrough. When selectively blocking fluid flow, for example, theflapper valve 67 can block a first flow of fluid (e.g., the downwardflow), and can allow a second flow of fluid (e.g., the upward flow).

FIG. 3 depicts another embodiment of the flapper valve assembly 30,which can include a line 302 extending between and operativelyconnecting a controller 304 and the pressurized chamber 71. Thecontroller 304 can be located at the surface of the wellbore or atanother remote location or can be proximal the flapper valve assembly30. Accordingly, to activate the flapper valve assembly 30, a signal canbe sent from the controller 304 through the line 302 and to the secondchamber 77 and/or the piston chamber 73. In one or more embodiments, thesignal can be pneumatic, hydraulic, or both, such that a higher or lowerpressure can be communicated through the line 302 into one of thechambers 73, 77, which can thereby allow one or both of the chambers 73,77 to act as the above-described pressurized chamber 71 (FIGS. 1-2). Forexample, the controller 304 can include a compressor such that, to movethe sleeve 70 from the first to the second position, the controller 304can send a high pressure flow through the line 302 and into the one ofthe chambers 73, 77. This can create a pressure differential across thepiston 90, thereby causing the sleeve 70 to slide upward, which canthereby release the flapper valve 67.

Furthermore, to re-stow the flapper valve 67, a flow can be evacuatedfrom the piston chamber 73 by the controller 304 via the line 302, forexample. This can provide a pressure differential in the reversedirection across the piston 90, which can cause the sleeve 70 to slideback down to stow the flapper valve 67. Although not shown, it will beappreciated that line 302 can include any valves, manifolds, headers,junctions, etc. as needed.

In one or more embodiments, the controller 304 can send an electricalsignal to components of the flapper valve assembly 30 to effect movementof the flapper valve 67. For example, the flapper valve assembly 30 caninclude an electromagnetic solenoid or the like (not shown), which canbe actuated to push or pull the sleeve 70 through its movement.Furthermore, the controller 304 can utilize wireless telemetry or wiredsignals to transmit instructions and can include any receiving devicespositioned proximal the flapper valve assembly 30 in the wellbore

FIG. 4 depicts a cross-sectional view of yet another embodiment of theflapper valve assembly 30. The flapper valve assembly 30 can besubstantially similar to the flapper valve assembly 30 described abovewith reference to FIGS. 1 and 2. Accordingly, the flapper valve assembly30 can include a flapper valve 67 and a sliding sleeve 70 that can slidefrom a first to a second position by hydrostatic force. In one or moreembodiments, the flapper valve 67 can have flat extents, as opposed tothe saddle-shaped flapper valve 67 described above. In one or moreembodiments, the flapper valve 67 can have a flat cross section, or canhave a dome shape interior (not shown) to support additional load. Inone or more embodiments, the flapper valve 67 can be similar to thatdescribed in U.S. patent application Ser. No. 11/010,072, the entiretyof which is incorporated herein by reference to the extent it is notinconsistent with this disclosure.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

Certain embodiments and features have been described using a set ofnumerical upper limits and a set of numerical lower limits. It should beappreciated that ranges from any lower limit to any upper limit arecontemplated unless otherwise indicated. Certain lower limits, upperlimits and ranges appear in one or more claims below. All numericalvalues are “about” or “approximately” the indicated value, and take intoaccount experimental error and variations that would be expected by aperson having ordinary skill in the art.

Various terms have been defined above. To the extent a term used in aclaim is not defined above, it should be given the broadest definitionpersons in the pertinent art have given that term as reflected in atleast one printed publication or issued patent. Furthermore, allpatents, test procedures, and other documents cited in this applicationare fully incorporated by reference to the extent such disclosure is notinconsistent with this application and for all jurisdictions in whichsuch incorporation is permitted.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A downhole tool, comprising: a tubular housing having an inner bore;a sleeve disposed in the inner bore and configured to slide between afirst position and a second position; a flapper valve pivotally coupledto the tubular housing, maintained in an inoperative position when thesleeve is in the first position, and pivotable between an open positionand a closed position when the sleeve is in the second position; and apressurized chamber in fluid communication with the sleeve, wherein,upon activation of the downhole tool, a hydrostatic pressure is appliedon the sleeve via the pressurized chamber, such that the sleeve slidesfrom the first position to the second position.
 2. The downhole tool ofclaim 1, wherein the tubular housing defines the pressurized chamber andfurther comprises a vented section extending between the inner bore andthe pressurized chamber, wherein activation includes removing the ventedsection to provide fluid communication between the inner bore and thepressurized chamber.
 3. The downhole tool of claim 2, wherein the ventedsection comprises a frangible material, a dissolvable material, or both.4. The downhole tool of claim 1, further comprising a controlleroperatively connected to the pressurized chamber via a controller line,wherein activation includes the controller causing an increased pressureto be applied to the pressurized chamber.
 5. The downhole tool of claim1, wherein the tubular housing further comprises: an upper sub in whichthe pressurized chamber is defined, wherein the upper sub provides aportion of the inner bore; and a lower sub coupled to the upper sub,wherein the lower sub provides another portion of the inner bore andprovides a valve seat, and wherein the flapper valve is pivotallycoupled to the lower sub.
 6. The downhole tool of claim 5, wherein: thetubular housing includes a storage cavity defined therein, wherein thestorage cavity is configured to receive the flapper valve in theinoperative position; and the sleeve includes a lower end configured toengage the lower sub when the sleeve is in the first position, whereinthe sleeve in the first position sealingly covers the storage cavity. 7.The downhole tool of claim 6, wherein the flapper valve issaddle-shaped, such that, when in the inoperative position, the flappervalve fits between substantially concentric cylindrical portions of thesleeve and the tubular housing in the storage cavity.
 8. The downholetool of claim 5, wherein the sleeve further comprises a piston having afirst side facing the lower sub and a second side facing the upper sub,the piston being coupled to the sleeve and slidably engaging the tubularhousing.
 9. The downhole tool of claim 8, further comprising: a pistonchamber defined in the tubular housing adjacent the first side of thepiston; and a line extending from the pressurized chamber to the pistonchamber, the line configured to provide fluid communication between thepressurized chamber and the piston chamber.
 10. The downhole tool ofclaim 9, further comprising a second chamber defined adjacent the secondside of the piston, wherein the piston is configured to slide toward theupper sub and reduce a volume of the second chamber when a pressure inthe piston chamber is increased.
 11. A method for plugging a casingstring with a flapper valve assembly, comprising: storing a flappervalve in a stowed position with a sleeve; biasing the flapper valvetoward a valve seat; longitudinally moving the sleeve by applying ahydrostatic pressure differential across the sleeve to release theflapper valve from the stowed position; and selectively blocking a flowof fluid through the casing string with the flapper valve.
 12. Themethod of claim 11, wherein longitudinally moving the sleeve comprisesincreasing a pressure on a side of the sleeve.
 13. The method of claim12, wherein increasing the pressure on the side of the sleeve comprises:perforating a tubular housing in which a pressurized chamber is defined,wherein, after the perforating, the pressurized chamber fluidlycommunicates with an inner bore of the tubular housing; andcommunicating a bore pressure of the inner bore to a side of the sleevevia the pressurized chamber.
 14. The method of claim 13, whereinlongitudinally moving the sleeve further comprises isolating a secondchamber disposed on a second side of the sleeve from the bore pressure,wherein a pressure in the second chamber is less than the bore pressure.15. The method of claim 13, wherein perforating the tubular housingcomprises dissolving a section of the tubular housing.
 16. The method ofclaim 11, wherein longitudinally moving the sleeve comprises applying apressure to a pressurized chamber with a controller in fluidcommunication with the pressurized chamber.
 17. A flapper valveassembly, comprising: a tubular housing connectable to a wellbore casingstring and having a storage cavity defined therein; a sleeve slidablebetween a first position and a second position, wherein the sleeve inthe first position covers the storage cavity and the sleeve in thesecond position at least partially uncovers the storage cavity; aflapper valve disposed in the tubular housing and pivotally connectedthereto, wherein the flapper valve is contained in the storage cavitywhen the sleeve is in the first position, and wherein the flapper valveis pivotable between an open position and a closed position when thesleeve is in the second position; and a pressurized chambercommunicating with the sleeve and configured to create a pressuredifferential across at least a portion of the sleeve, such that thesleeve moves longitudinally from the first position to the secondposition.
 18. The flapper valve assembly of claim 17, furthercomprising: a piston having opposing first and second sides, wherein thepiston is coupled to the sleeve and located between the sleeve and thetubular housing; and a piston chamber fluidly communicating with thepressurized chamber and defined in the tubular housing adjacent thefirst side of the piston.
 19. The flapper valve assembly of claim 18,further comprising a second chamber isolated from the pressurizedchamber and defined at least partially in the tubular housing adjacentthe second side of the piston, wherein, when the tubular housing isvented to communicate the inner bore with the pressurized housing, apressure in the second chamber is less than a pressure in the pistonchamber.
 20. The flapper valve assembly of claim 18, wherein the tubularhousing further comprises a dissolvable section, a frangible section, orboth, which is removable to provide fluid communication between theinner bore and the pressurized chamber.